A laser diode for working, a CPU (Central Processing Unit) of a computer, or a power converter such as an inverter generates heat as it is driven. Such a component may be damaged or performance thereof may deteriorate due to heat generated by the component itself. In addition, parts arranged around a heat generator may adversely be affected. Such a heat generator is cooled by a cooler for heat removal.
Some coolers include a heat sink, the heat sink having fins. Fins are formed in the heat sink so that a heat transfer area for radiation increases and hence efficiency in heat exchange can be improved.
Japanese Patent Laying-Open No. 2001-352025 discloses a heat generator cooling device, in which a heat generator is arranged in a heat sink and a coolant water is supplied to a channel group formed of fins of the heat sink and a base. In this heat generator cooling device, an inlet port for supplying the coolant water to the channel group is provided, an inlet side header is provided between the inlet port and the channel group, and an outlet side header is provided downstream of the channel group. According to this disclosure, relation of Wb>Wc>Wa is set, where Wb represents a width of a channel closer to the inlet port, Wc represents a width of a channel farther from the inlet port, and Wa represents a width of a channel in the center. According to the disclosure, this heat generator cooling device can achieve uniform cooling of the heat generator.
Japanese Patent Laying-Open No. 5-206339 discloses a radiator including a plurality of fins on a surface of a base, the fins being arranged at a regular pitch and the fins different in thickness being arranged such that the fin located at an edge of the base is largest in thickness and the fin located at the center of the base is smallest in thickness. According to the disclosure, in this radiator, a uniform flow velocity can be provided to each fin in the radiator and an effect of cooling by the fins can be maximized without increasing a dimension of the radiator as a whole.
Japanese Patent Laying-Open No. 9-23081 discloses a boiling cooling device. The boiling cooling device is disclosed, in which partition walls partitioning a cooling pool into three coolant chambers in correspondence with IGBT (Insulated Gate Bipolar Transistor) modules attached to a surface and a plurality of coolant flow control plates vertically dividing a boiling region of each coolant chamber are provided in the cooling pool. The coolant flow control plates are provided in the boiling region at regular intervals in a vertical direction in an inclined manner. In addition, in each coolant chamber partitioned by the partition walls, an outlet passage through which vapor resulting from boiling flows out is provided on one side of the boiling region, and an inlet passage through which a condensate flows in is provided on the other side thereof. According to the disclosure, this boiling cooling device can prevent lowering in radiation performance on an upper side of the boiling region in the coolant pool.
Japanese Patent Laying-Open No. 2004-134742 discloses a device for cooling electronic components, in which a liquid cooling portion and an air cooling portion are integrally formed and a heat absorption surface of the liquid cooling portion is joined to a heat generating part that locally generates heat. A liquid cooling pump for circulating a coolant through a flow passage is provided in the liquid cooling portion. According to the disclosure, this device for cooling electronic components is excellent in heat conduction efficiency and radiation performance.
Japanese Patent Laying-Open No. 2005-116877 discloses a cooling system, in which a maximum radiation amount of a radiator is not higher than a maximum amount of heat generated by an IGBT. According to the disclosure, the radiator for radiating heat absorbed from a heat generator such as an IGBT can be made smaller in size in the cooling system.
As disclosed, for example, in Japanese Patent Laying-Open No. 2001-352025 above, a cooler in which a flow path of a coolant is formed by fins is available. In this cooler, a space between the fins serves as the flow path of the coolant. In this cooler, heat exchange is carried out while the coolant flows along a main surface of the fin.
In each flow path of the coolant, pressure becomes lower toward downstream because of pressure loss. Here, originating from manufacturing errors or the like, a structure of a flow path may differ. Magnitude of pressure loss in each flow path may differ, which may result in a different flow rate of the coolant that flows through each flow path. Consequently, cooling may not be uniform at the surface of the cooler. For example, when a flow rate transiently fluctuates, variation in pressure loss is different in each flow path and hence it is difficult to achieve a uniform flow rate in the flow paths.
In addition, a boundary layer of the coolant is formed on the surface of the fin. As the boundary layer becomes greater (thicker) toward downstream, heat transfer becomes poorer and cooling capability is lower toward downstream. Therefore, cooling capability may be different between an upstream area and a downstream area of the flow path of the coolant.
In an example where the cooler is a boiling-type cooler, a ratio of gas phase to liquid phase is higher toward downstream of the flow path. Heat transfer becomes poorer and cooling capability becomes lower toward downstream of the flow path. In particular, if a flow rate of the coolant to each flow path is different, a downstream area of the flow path where the flow rate has decreased is extremely short of a liquid coolant and burnout which will be described later is more likely.
Moreover, in the case of a boiling-type cooler, what is called burnout, in which transition from a nucleate boiling state to a film boiling state is made, is more likely toward downstream of the flow path. When burnout occurs, heat transfer becomes poorer. This tendency is more likely as a cross-sectional area of the flow path of the coolant is smaller. For example, in a cooler having a microchannel structure, a flow path has a small diameter and hence the flow path may be blocked by vapor phase. Thus, cooling capability is lower toward downstream.